# 实例21
# 共有x个桃子
# x2 = 1
# for day in range(9):
#     x1 = (x2 + 1) * 2
#     x2 = x1
# print (x1)
# 实例22
# for i in range(ord('x'), ord('z') + 1):
#     for j in range(ord('x'), ord('z') + 1):
#         if i != j:
#             for k in range(ord('x'), ord('z') + 1):
#                 if (i != k) and (j != k):
#                     if (i != ord('x')) and (k != ord('x')) and (k != ord('z')):
#                         print('order is a -- %s\t b -- %s\tc--%s' % (chr(i), chr(j), chr(k)))
# 实例23
# for i in range(8):
#     if i<4:
#         s=' '*(4-i)+'*'*(2*i-1)
#     else:
#         s=' '*(i-4)+'*'*(2*(4-i)+7)
#     print(s)
# 实例24
# fenzi=[2,3]
# fenmu=[1,2]
# ans=0
# for i in range(2,20):
#     fenzi.append((fenzi[i-1]+fenzi[i-2]))
#     fenmu.append((fenmu[i-1]+fenmu[i-2]))
# for i in range(len(fenzi)):
#     ans+=fenzi[i]/fenmu[i]
# print(ans)
# 实例25
# ans=0
# cur=1
# for i in range(1,21):
#     cur*=i
#     ans+=cur
# print(ans)
# 实例26
# def f(x):
#     if x==1:
#         return 1
#     else:
#         return x*f(x-1)
# print(f(5))
# 实例27
# a=[]
# for i in range(5):
#     a.append(int(input()))
# def f(n):
#     if n>=5:
#         return
#     if n<5:
#         f(n+1)
#         print(a[n])
# f(0)
# 实例28
# def f(n):
#     if n==5:
#         return 10
#     return f(n+1)+2
# print(f(1))
# 实例29
# s=int(input())
# a=str(s)
# print(len(a),a[::-1])
# 实例30
# s=input()
# i=0
# j=len(s)-1
# while i<j:
#     if s[i]!=s[j]:
#         print('false')
#         break
#     i+=1
#     j-=1
# else:
#     print('true')
